Distant retrograde orbit

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The Earth-Moon Lagrange points

A distant retrograde orbit (DRO), as most commonly conceived, is a spacecraft orbit around a moon that is highly stable because of its interactions with two Lagrange points (L1 and L2) of the planet–moon system.


In more general terms, an object of negligible mass can be in a DRO around the smaller body of any two-body system, such as planet–Sun or exoplanet–star.

Using the example of a spacecraft in a DRO around a moon, the craft would orbit in the direction opposite to the direction in which the moon orbits the planet. The orbit is "distant" in the sense that it passes above the Lagrange points, rather than being near the moon. If we consider more and more distant orbits, the synodic period (the period between two moments when the craft passes between the planet and the moon) gets longer and approaches that of the moon going around the planet, so that the sidereal period (the time it takes for the craft to come back to a given constellation as viewed from the moon) can become much longer than the orbital period of the moon. A hypothetical example with Europa has a sidereal period about eight times the orbital period of Europa. [1]

DROs have been researched for several decades, but in 2022, NASA's Orion Spacecraft entered the orbit during the Artemis 1 mission and it was speculated that the Chang'e 5 orbiter may also have now done so. [2]


The stability of a DRO is defined in mathematical terms as having very high Lyapunov stability, where an equilibrium orbit is "locally stable if all solutions which start near the point remain near that point for all time". [1]

List of objects in distant retrograde orbit

Chang'e 5 orbiter

Chang'e 5 spacecraft with orbiter at bottom Chang-e-5-zh-2.png
Chang'e 5 spacecraft with orbiter at bottom

After dropping off return samples for Earth, China's Chang'e 5 (CE-5) orbiter first moved to Sun-Earth Lagrange point 1 (L1) in March 2021 for solar observations. [3] In January 2022, CE-5 left L1 point for the lunar distant retrograde orbit (DRO) to conduct very-long-baseline interferometry tests in preparation for the next stage of China's lunar exploration program. [3] [4] According to The Space Review (TSR), this maneuver was depicted in Chinese government and academic documents. [2] In February 2022, Multiple amateur satellite trackers observed CE-5 had entered DRO, which was the first spacecraft in history to utilize the orbit. [3]

Orion spacecraft

Orion spacecraft prior to arriving at the Moon, where it would later get into DRO Orion Artemis I Selfie 1.jpg
Orion spacecraft prior to arriving at the Moon, where it would later get into DRO

On 16 November 2022, the Space Launch System was launched from Complex 39B as part of the Artemis 1 mission carrying Orion to the moon. [5] [6] On 25 November it entered DRO and orbited the Moon in that orbit. [7] [8]

Space concepts proposed to use a DRO

Jupiter Icy Moons Orbiter

A distant retrograde orbit was one of the proposed orbits around Europa for the Jupiter Icy Moons Orbiter—principally for its projected stability and low-energy transfer characteristics—but that mission concept was cancelled in 2005. [1]

Asteroid Redirect Mission (ARM)

A distant retrograde orbit was considered to be used for the proposed Asteroid Redirect Mission. Although the mission would end up getting cancelled, the research done with DRO in-mind, lead to the orbit being used for Artemis 1. [9]

NASA Lunar Gateway

Two system requirements for the NASA Lunar Gateway, as published in the Baseline DSG-RQMT-001 [10] published in June 2019, mention the use of lunar DROs. Requirement L2-GW-0029, Single Orbit Transfer, states "the Gateway shall be capable of performing a single round trip transfer to Distant Retrograde Orbit (DRO) and back within 11 months". Requirement L2-GW-0026, Propulsion System Capability, states "the Gateway shall provide a fuel capacity that would support performing a minimum of two round-trip uncrewed low-energy cislunar orbit transfers between a near-rectilinear halo orbit (NRHO) and a distant retrograde orbit (DRO) and orbit maintenance for a period of 15 years between refueling". Although the selected orbit for the Gateway has been confirmed to be NRHO [11] instead of DRO.

DRO orbits in fiction

In the 2019 Daniel Suarez novel Delta-v, a 560-tonne crewed asteroid-mining ship Konstantin is constructed in a lunar DRO approximately 40,000 km (25,000 mi) above the Moon. [12]

See also

Related Research Articles

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The Crew Exploration Vehicle (CEV) was a component of the U.S. NASA Vision for Space Exploration plan. A competition was held to design a spacecraft that could carry humans to the destinations envisioned by the plan. The winning design was the Orion spacecraft.

<span class="mw-page-title-main">NASA</span> American space and aeronautics agency

The National Aeronautics and Space Administration is an independent agency of the U.S. federal government responsible for the civil space program, aeronautics research, and space research. Established in 1958, NASA succeeding the National Advisory Committee for Aeronautics (NACA), to give the U.S. space development effort a distinctly civilian orientation, emphasizing peaceful applications in space science. NASA has since led most American space exploration, including Project Mercury, Project Gemini, the 1968–1972 Apollo Moon landing missions, the Skylab space station, and the Space Shuttle. NASA currently supports the International Space Station and oversees the development of the Orion spacecraft and the Space Launch System for the crewed lunar Artemis program, the Commercial Crew spacecraft, and the planned Lunar Gateway space station.

<span class="mw-page-title-main">Artemis 1</span> 2022 uncrewed Moon-orbiting NASA mission

Artemis 1, officially Artemis I and formerly Exploration Mission-1 (EM-1), was an uncrewed Moon-orbiting mission. As the first major spaceflight of NASA's Artemis program, Artemis 1 marked the agency's return to lunar exploration after the conclusion of the Apollo program five decades earlier. It was the first integrated flight test of the Orion spacecraft and Space Launch System (SLS) rocket, and its main objective was to test the Orion spacecraft, especially its heat shield, in preparation for subsequent Artemis missions. These missions seek to reestablish a human presence on the Moon and demonstrate technologies and business approaches needed for future scientific studies, including exploration of Mars.

<span class="mw-page-title-main">Subsatellite</span> A satellite that orbits a natural satellite

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<span class="mw-page-title-main">Asteroid Redirect Mission</span> 2013–2017 proposed NASA space mission

The Asteroid Redirect Mission (ARM), also known as the Asteroid Retrieval and Utilization (ARU) mission and the Asteroid Initiative, was a space mission proposed by NASA in 2013; the mission was later cancelled. The Asteroid Retrieval Robotic Mission (ARRM) spacecraft would rendezvous with a large near-Earth asteroid and use robotic arms with anchoring grippers to retrieve a 4-meter boulder from the asteroid.

<span class="mw-page-title-main">Artemis 2</span> Artemis programs second lunar flight

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<span class="mw-page-title-main">Artemis 3</span> Third orbital flight of the Artemis program

Artemis 3 is planned as the first crewed Moon landing mission of the Artemis program and the first crewed flight of the Starship HLS lander. Artemis 3 is planned to be the second crewed Artemis mission and the first crewed lunar landing since Apollo 17 in December 1972. Originally scheduled to be launched in 2024, as of June 2023, the mission is likely not to take place before 2026.

<span class="mw-page-title-main">Lunar Gateway</span> Lunar orbital space station under development

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<span class="mw-page-title-main">EQUULEUS</span> Japanese nanosatellite

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<span class="mw-page-title-main">Artemis program</span> NASA-led lunar exploration program

The Artemis program is a robotic and human Moon exploration program led by the United States' National Aeronautics and Space Administration (NASA) along with six major partner agencies— the European Space Agency (ESA), the Japan Aerospace Exploration Agency (JAXA), the Canadian Space Agency (CSA), the Israel Space Agency (ISA) and the Australian Space Agency (ASA), (ISRO) Indian Space Research Organisation. The Artemis program is intended to reestablish a human presence on the Moon for the first time since the Apollo 17 mission in 1972. The main parts of the program are the Space Launch System (SLS), the Orion spacecraft, the Lunar Gateway space station, and the commercial Human Landing Systems. The program's long-term goal is to establish a permanent base on the Moon to facilitate the feasibility of human missions to Mars.

<span class="mw-page-title-main">Artemis 4</span> Fourth orbital flight of the Artemis program

Artemis 4 is the fourth planned mission of NASA's Artemis program. The mission will launch four astronauts on a Space Launch System rocket and an Orion to the Lunar Gateway and the second lunar landing of the Artemis program.

<span class="mw-page-title-main">Artemis 5</span> Fifth orbital flight of the Artemis program

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<span class="mw-page-title-main">CAPSTONE</span> NASA satellite to test the Lunar Gateway orbit

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<span class="mw-page-title-main">Power and Propulsion Element</span> Power and propulsion module for the Gateway space station

The Power and Propulsion Element (PPE), previously known as the Asteroid Redirect Vehicle propulsion system, is a planned solar electric ion propulsion module being developed by Maxar Technologies for NASA. It is one of the major components of the Gateway. The PPE will allow access to the entire lunar surface and a wide range of lunar orbits and double as a space tug for visiting craft.


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  2. 1 2 Burke, Kristin (11 April 2022). "The Space Review: What is China doing at the lunar distant retrograde orbit?". The Space Review . Archived from the original on 2022-04-12. Retrieved 2022-04-12.
  3. 1 2 3 Jones, Andrew (15 February 2022). "A Chinese spacecraft is testing out a new orbit around the moon". Space News.
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  9. NASA [@NASA] (19 November 2022). "@JVendl @NASA_Orion We first studied the DRO to support the proposed Asteroid Redirect Mission (ARM) which paralleled early SLS and Orion development. The plan for ARM was to capture a near Earth asteroid and redirect it to a lunar DRO. (1/4)" (Tweet). Retrieved 2 December 2022 via Twitter.
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  12. Suarez, Daniel (2019). Delta-v. New York: Penguin Random House. pp. 189–198. ISBN   978-1524742416.